Processes for synthesizing borohydride compounds

ABSTRACT

The present invention relates to processes for producing borohydride compounds. In particular, the present invention provides efficient processes and compositions for the large-scale production of borohydride compounds of the formula YBH 4  by the reaction of a boron-containing compound represented by the formula BX 3  with hydrogen or an aldehyde to obtain diborane and HX, and reacting the diborane with a Y-containing base selected from those represented by the formula Y 2 O, YOH and Y 2 CO 3  to obtain YBH 4  and YBO 2 . Y is selected from the group consisting of the alkali metals, pseudo-alkali metals, alkaline earth metals, an ammonium ion, and quaternary amines of the formula NR 4   + , wherein each R is independently selected from hydrogen and a straight- or branched-chain C 1-4  alkyl group, and X is selected from the group consisting of halide ions, —OH, —R′ and —OR′ groups, chalcogens, and chalcogenides, wherein R′ is a straight- or branched-chain C 1-4  alkyl group.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/833,904, filed Apr. 12, 2001 now U.S. Pat. No. 6,524,542 andU.S. patent application Ser. No. 10/116,767, filed Apr. 4, 2002 nowPreexam Processing which, in turn, is a divisional application of U.S.patent application Ser. No. 09/710,041, filed Nov. 8, 2000, now U.S.Pat. No. 6,433,129, issued Aug. 13, 2002.

FIELD OF THE INVENTION

The present invention relates to processes for producing borohydridecompounds. In particular, the present invention provides efficientprocesses for the large-scale production of borohydride compounds.

BACKGROUND OF INVENTION

Environmentally friendly fuels, e.g., alternative fuels to hydrocarbonbased energy sources, are currently of great interest. One such fuel isborohydride, which can be used directly as an anodic fuel in a fuel cellor as a hydrogen storage medium, e.g., hydrogen can be liberated by thereaction of sodium borohydride with water, which produces sodium borateas a byproduct. As with all fuels, borohydride must be manufactured fromreadily available materials. Thus, there is a need for improved andenergy efficient industrial scale manufacturing processes for producingborohydride compounds.

Typical industrial processes for the production of sodium borohydrideare based on the Schlesinger process (Equation 1) or the Bayer process(Equation 2), which are both described below. Equation 1 illustrates thereaction of alkali metal hydrides with boric oxide, B₂O₃, or trimethylborate, B(OCH₃)₃, at high temperatures, e.g., ca. 330° to 350° C. forB₂O₃ and 275° C. for B(OCH₃)₃.

4NaH+B(OCH₃)₃→3NaOCH₃+NaBH₄  (1)

 Na₂B₄O₇+16Na+8H₂+7SiO₂→4NaBH₄+7Na₂SiO₃  (2)

The primary energy cost of these processes stems from the requirementfor a large amount of sodium metal, e.g., 4 moles of sodium per mole ofsodium borohydride produced. Sodium metal is commercially produced byelectrolysis of sodium chloride with an energy input equivalent to about37,500 BTU (39,564 KJ) per pound of sodium borohydride produced. Incontrast, the hydrogen energy stored in borohydride is about 10,752 BTU(11,341 KJ) of hydrogen per pound of sodium borohydride. The Schlesingerprocess and the Bayer process, therefore, do not provide a favorableenergy balance, because the energy cost of using such large amounts ofsodium in these reactions is high compared to the energy available fromsodium borohydride as a fuel.

Furthermore, in view of the large quantities of borohydride needed foruse, e.g., in the transportation industry, these processes would alsoproduce large quantities of NaOCH₃ or Na₂SiO₃ waste products. Sincethese byproducts are not reclaimed or reused, further energy and/orexpense would need to be expended to separate and properly dispose ofthese materials.

Typical improvements of the prior art describe simple modifications ofthe two processes given in equations (1) and (2). As such, however,these improvements also suffer from the disadvantages stated above anddo not provide any improved energy efficiency. It can be seen,therefore, that the widespread adoption of borohydride as a source ofhydrogen would almost necessitate a recycle process that would allow theregeneration of borohydride from the borate byproduct. Thus, borohydridecan be used as a fuel, and the resulting borate can then be recycledback to generate borohydride. However, such a process cannot rely on thesame sodium stoichiometry shown in the current borohydride manufactureprocesses, e.g., the Schlesinger process of Equation (1) or the Bayerprocess of Equation (2).

The present invention provides processes for producing large quantitiesof borohydride compounds, which overcome the above-describeddeficiencies. In addition, the efficiencies of the processes of thepresent invention can be greatly enhanced over the typical processes forproducing borohydride compounds.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a process is provided forproducing borohydride compounds, which includes reacting theboron-containing compound BX₃ with hydrogen to obtain diborane (B₂H₆)which, is turn, reacted with a Y-containing base selected from thoserepresented by the formulae Y₂O, Y₂CO₃ and YOH to obtain YBH₄ and aYBO₂, wherein Y is selected from the group consisting of the alkalimetals, pseudo-alkali metals, alkaline earth metals, an ammonium ion,and quaternary amines of formula NR₄ ⁺, wherein each R is independentlyselected from hydrogen and straight- or branched-chain C₁₋₄ alkylgroups; and X is selected from the group consisting of halide ions,hydroxyl, alkyl or alkoxy groups, chalcogens, and chalcogenides.

In another embodiment of the present invention, a process is providedfor producing borohydride compounds, which includes reacting aboron-containing compound of the formula BX₃ with a Y-containing base ofthe formula YH to obtain YHBX₃; and separately reacting BX₃ withhydrogen to obtain diborane which is, in turn, reacted with YHBX₃ toobtain YBH₄ and BX₃, wherein X and Y are as defined above.

In either of these embodiments, the Y-containing base of the formula Y₂Oand the boron-containing compound of the formula BX₃ can be obtained bythe following processes. The first process includes: (A) reacting aborate of the formula YBO₂ with CO₂ and H₂O to obtain YHCO₃, and borax;(B) heating YHCO₃ to obtain Y₂O, CO₂ and H₂O; (C) separately reactingborax with an acid to obtain boric acid B(OH)₃ which is isolated anddehydrated to B₂O₃; (D) reacting the B₂O₃ with carbon and X₂ to obtainBX₃ and CO₂. The second process includes: (I) reacting a borate of theformula YBO₂ with CO₂ and an alcohol to obtain YHCO₃ and B(OR)₃ whereinR is a lower alkyl group; (II) heating YHCO₃ to obtain Y₂O, CO₂ and H₂O;(III) reacting the B(OR)₃ with H₂O to obtain B(OH)₃, which is dehydratedto form B₂O₃; and (IV) reacting the B₂O₃ with carbon and X₂ to obtainBX₃ and CO₂. The Y-containing base compounds of the formula Y₂CO₃ can beobtained by replacing steps (B) and (II) with the following step (B2):converting the YHCO₃ to Y₂CO₃, CO₂ and H₂O. Alternatively, theboron-containing compounds BX₃ can be obtained by replacing steps (C)and (D) with one of the following steps: (Cl) where X is a halide,reacting borax with carbon and X₂ to obtain BX₃ and CO₂; or (C2), whereX is an alkoxy group, reacting borax with an alcohol to obtain BX₃.

In still another embodiment of the present invention, a process isprovided for producing borohydride compounds, which includes: (A)reacting a borate of the formula YBO₂ with CO₂ and H₂O to obtain YHCO₃and a B₂O₃ compound; (B) heating the YHCO₃ to obtain Y₂O, CO₂, and H₂O;(C) reacting the B₂O₃ compound with an alcohol to obtain BX₃; (D)reacting methane with the Y₂O to obtain Y, carbon monoxide and H₂; (E)reacting the Y with H₂ to obtain YH; (F) reacting the BX₃ with the YH toobtain YHBX₃; (G) separately reacting BX₃ with H₂ to obtain B₂H₆ and HX;and (H) reacting the YHBX₃ with B₂H₆ to obtain YBH₄ and BX₃ wherein Yand X are as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the present invention will be morefully appreciated from a reading of the detailed description whenconsidered with the accompanying drawings wherein:

FIG. 1 is a flow diagram, which illustrates one embodiment for producingborohydride compounds in accordance with the present invention; and

FIG. 2 is a flow diagram, which illustrates another embodiment forproducing borohydride compounds in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes processes for producing borohydridecompounds from sodium borate or sodium borate ores, such as borax(referred to herein as “borate compounds”). Each step of these processescan be conducted in a batchwise or continuous manner, as is well-knownto the skilled artisan. The term “about,” as used herein, means +10% ofthe stated value.

The overall cost of producing borohydride compounds is net hydrogenationof a borate compound, such as, sodium borate, borax ore, or higherborates of the formula Na₂O.xB₂O₃, where x is 2 to 5, such as,tetraborate and pentaborate, to give sodium borohydride and water asshown in equation (3).

NaBO₂+H₂→NaBH₄+H₂O  (3)

The hydrogen can be obtained from any suitable source, as is well knownto one skilled in the art. Where the hydrogen gas is liberated by thesteam reformation of methane, for example, the net reaction can berepresented as illustrated in equation (4):

NaBO₂+CH₄→NaBH₄+CO₂  (4)

These processes eliminate the dependence on large quantities of sodiummetal that exists in current industrial processes for borohydridesynthesis, thereby removing a large energy cost in borohydrideproduction. In addition, these processes can allow for recycle of excessreagents and byproducts produced within the process in order to providegreater efficiency in the production of sodium borohydride.

The basic starting material of the present process is a borate compound,e.g., YBO₂, wherein Y is selected from the group consisting of H⁺,alkali metal ions, e.g., Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Fr⁺; pseudo-alkalimetal ions, e.g., Tl⁺; an ammonium ion (NH₄ ⁺); alkaline earth metalions, e.g., Be⁺⁺, Mg⁺⁺, Ca⁺⁺, Sr⁺⁺, and Ba⁺⁺; and quaternary aminesrepresented by the formula NR₄ ⁺, wherein each R is independentlyselected from hydrogen and straight- or branched-chain C₁₋₄ alkylgroups. Y is preferably selected from the group consisting of Na⁺, Li⁺,K⁺, Mg⁺⁺, and Ca⁺⁺, most preferably Na⁺ or Li⁺. Alternatively, thestarting material YBO₂ can be replaced with other sodium boratesrepresented by the formula Na₂O·xB₂O₃, wherein x is 1 to 5, or hydratedborates represented by the formula Na₂O·xB₂O₃·yH₂O, wherein y is 0.5 to10, e.g. Na₂O·2B₂O₃·5H₂O, also represented as Na₂B₄O₇·5H₂O. overall,there starting materials can be expressed as Na₂O·xB₂O₃·yH₂O wherein xis 1-5 and y with 0-10 wherein y is zero representing the non-hydratedborates.

From the starting material of a borate compound, such as YBO₂, reactionscan be conducted to create a Y-containing base, e.g., Y₂O, and aboron-containing compound, e.g., BX₃, wherein X is selected from thegroup consisting of halide ions, i.e. F, Cl, Br, I, and At; —OH, R′ or—OR′ groups; chalcogens, i.e. O, S, Se, Te, and Po; and thechalcogenides, such as —SR, —SeR, and —TeR, wherein R is as definedabove and R′ is a straight- or branched-chain C₁₋₄ alkyl group. Inaccordance with the present invention, X is preferably a halide ion oran alkoxy group.

For example, in one embodiment of the process of the invention wherein Xis an alkoxy group, the Y-containing base and the boron-containingcompound can be obtained by the following set of chemical reactions (5a)to (5c). In equation (Sc), the conversion of YHCO₃ to Y₂O, carbondioxide and water is carried out by heating to a temperature of fromabout 400° C. to about 1000° C.:

4YBO₂+2CO₂+H₂O→2YHCO₃+Y₂O·2B₂O₃  (5a)

Y₂O·2B₂O₃+12HX→4BX₃+2YOH+5H₂O  (5b)

2YHCO₃→Y₂O+2CO₂+H₂O  (5c)

2YOH→Y₂O+H₂O  (5d)

The above set of reactions illustrates when Y is chosen to have a 1⁺valence. When Y is chosen to have a 2⁺ valence, the stoichiometry can beadjusted accordingly. Such obvious changes in stoichiometry would beclearly evident to the skilled artisan. All of the following reactionsassume that Y is chosen to have a valence of 1⁺.

The reaction of equation (5c) can be substituted with the followingreaction of equation (5ci).

2YHCO₃→Y₂CO₃+H₂O+CO₂  (5ci)

The conversion shown in equation (5ci) can be conducted at a much lowertemperature than equation (5c), i.e. a temperature from about 50° toabout 120° C. The conversion is carried out in an appropriate apparatus,such as a rotary drier. The solid Y₂CO₃ can be removed from the gaseousmixture of water and carbon dioxide by any method and/or process knownto the skilled artisan.

After the Y-containing base and the boron-containing compound have beenobtained, a Y-borohydride can be formed by a variety of processes. Inone embodiment, the Y-borohydride can be obtained by the reactions ofthe following set of equations (6a) to (6g):

CH₄+Y₂O→2Y+CO+2H₂  (6a)

2Y+H₂→2YH  (6b)

2BX₃+2YH→2YHBX₃  (6c)

CH₄+H₂O→3H₂+CO  (6d)

2CO+2H₂O→2H₂+2CO₂  (6e)

 2BX₃+6H₂→B₂H₆+6HX  (6f)

2YHBX₃+B₂H₆→2YBH₄+2BX₃  (6g)

Note that, if hydrogen is obtained from commercial sources, reactions(6d) and (6e) can be optional. In another embodiment, the Y-borohydridecan be obtained by substituting reaction (6g) with the followingreaction (6gi):

2Y₂O+2 B₂H₆→3YBH₄+YBO₂  (6gi)

Alternatively, reaction (6h) below can be substituted for the reactions(6f) and (6g):

2YHBX₃+6H₂→2YBH₄+6HX  (6h)

Additionally, instead of hydrogen in equation (6f), BX₃ can be reactedwith an aldehyde, such as formaldehyde (CH₂O), benzaldehyde (C₆H₅CHO),or acetaldehyde (CH₃CHO) in the presence of a copper metal catalyst.These aldehyde reactions can be run in an appropriate pressurizedapparatus, such as an autoclave, at about 380° to about 420° C. Oneskilled in the art would recognize that the stoichiometry of equation(9f) would have to be adjusted accordingly.

If the reaction of equation (5ci) described above is used, the reactionof equation (6a) can be substituted with the following reaction ofequation (6ai).

Y₂CO₃+2C→2Y+3CO  (6ai)

The reaction of equation (6ai) can be conducted by adding heat in thepresence of carbon, as is described in Hughes, “Production of theBoranes and Related Research,” pp. 12.

The overall process of this embodiment, with or without the alternativesubstitute reaction, results in the following net reaction (7):

YBO₂+CH₄→YBH₄+CO₂  (7)

In another embodiment, halogens, i.e. F₂, Cl₂, Br₂, I₂, and At₂, can beused in a variation of the embodiment using equations (5a) to (5c) toobtain the Y-containing bases and the boron-containing compound. In thisembodiment, equation (5b) is replaced with equations (5e) to (5g) below:

Y₂O·2B₂O₃+2HX+5H₂O→4B(OH)₃+2YX  (5e)

4B(OH)₃→2B₂O₃+6H₂O  (5f)

B₂O₃+3/2C+3X₂→2BX₃+3/2CO₂  (5g)

wherein C is carbon, and X is a F, Cl, Br, I, or At ion, preferably Clor Br. Alternatively, the carbon can be replaced with methane asillustrated by equation (5h) below:

B₂O₃+3/2CH₄+3X₂→2BX₃+3/2CO₂+H₂  (5h)

wherein X is F, Cl, Br, I, or At ions, preferably a Cl or Br ion.

When the halogen embodiment is utilized in conjunction with equations(6a) to (6g) to obtain the Y-borohydride, the halogen can optionally bereclaimed for reuse from the HX produced in the reaction of equation(6f) as illustrated in equation (8) below:

6HX+3/2O₂+CuX (solid)→3X₂+3H₂O  (8)

wherein CuX is a catalyst that is not consumed in the process, and X inCuX is Cl, Br, or I.

Any of the above-described processes of obtaining a Y-containing baseand a boron-containing compound can be used with any of theabove-described processes for obtaining a Y-borohydride.

In still another embodiment of the present invention, X can beindependently chosen to be different throughout a complete process,i.e., a particular process for obtaining a Y-containing base and aboron-containing compound, as described above, in combination with aparticular process for obtaining a Y-borohydride, as described above.When X is changed in a complete process, it is preferable to choose thedifferent X's to promote regeneration and use of a product as a reactantin a different reaction.

For example, in a combination of equations (5a) to (5c) and equations(6a) to (6g), or a combination of equations (5e) to (5g) and equations(6a) to (6g), X can be chosen to be a halide, e.g. F, Cl, Br, I, or At,in equations (6c) and (9f). This would allow recycling of the HXproduced in equation (6f) for use in equation (5e). Similarly, X can beseparately chosen to be an alkoxy, e.g., —OCH₃, for equations (6c) and(6g). This would allow recycling of the BX₃ produced in equation (6g)for use in equation (6c).

In an embodiment of the present invention, as illustrated in FIG. 1,YBO₂ is chosen to be sodium borate and HX is chosen to be HOR, i.e. analcohol. The sodium borate and the alcohol are reacted to produce atrialkyl borate. A portion of the trialkyl borate is converted to alkalimetal trialkoxy borohydride, and the remainder converted to diborane.The trialkoxy borohydride and the diborane can then be reacted to formthe desired borohydride compound. This process can be further describedin part by the following set of chemical reactions and formulae.

First, sodium borate from rotary dryer 50 can be reacted with ethanol inan appropriate reactor, as provided in equation (9).

NaBO₂+CO₂+3EtOH→NaHCO₃+B(OEt)₃+H₂O  (9)

For example, this reaction can be performed in a heated reactor with arotary mixer 70, such as a PORCUPINE PROCESSOR produced by The BethlehemCorporation of Easton, Pa., as illustrated in FIG. 1. In such anapparatus, a slurry of sodium borate and ethanol can be stirred togetherby a heated screw, which allows mixing of the reagents at temperaturesranging from about room temperature to about 70° C., preferably fromabout 50° C. to about 70° C. and pressures from about 0 to about 100 psi(6.8 atm.), preferably from about 1 to about 2 atm. Acids such asinorganic mineral acids or organic acids, PTFE beads, or carbon dioxideas shown in equation (9), are added to promote the reaction. In acontinuous process, the reagents are introduced into one end of thereactor, and the trialkoxy borane can be removed by distillation as itforms. Depending on the choice of acid, various sodium salts, such asNaHCO₃, are produced and can be separated to use as reactant in anotherreaction within the process.

For process convenience, the reaction of equation (9) may be carried outalternatively in two separate steps: first converting NaBO₂ to borax(Na₂O·2B₂O₃) in water (Equation 9a), then converting borax to B(OEt)₃ inethanol (Equation 9b).

4NaBO₂+2CO₂+H₂O→2NaHCO₃+Na₂O·2B₂O₃  (9a)

Na₂O·2B₂O₃+12EtOH→4 B(OEt)₃+2NaOH+5H₂O  (9b)

After separation in an appropriate apparatus, such as a centrifuge 80,the triethyl borate can be dried in an appropriate apparatus, such as adistillation unit 110. The water can be recycled for use in otherchemical reactions. All or a portion of the dried triethy lborate,B(OEt)₃ is then reacted with sodium hydride in an appropriate apparatusto provide sodium triethoxy borohydride, NaHB(OEt)₃, as provided inequation (10).

B(OEt)₃ (excess)+NaH→NaHB(OEt)₃  (10)

An important distinction should be drawn between equation (10) in thepresent invention and the Schlesinger process. In the Schlesingerprocess, trimethyl borate is added to excess sodium hydride (NaH), andthe reaction driven to yield sodium borohydride and sodium methoxide.The excess NaH is utilized to ensure that all intermediate boranecompounds are reduced completely to borohydride. In an example of theprocesses of the present invention, however, an alkali metal hydride,e.g., sodium hydride, can be added to excess trialkyl borate, e.g.,triethyl borate, and the reaction only proceeds to form an alkali metaltrialkoxyborohydride, e.g., sodium triethoxyborohydride, NaBH(OEt)₃.

The reaction of equation (10) is exothermic. For example, this reactioncan be performed in a gravity bed reactor 190, as illustrated in FIG. 1.In such an apparatus, excess liquid triethyl borate can be added tosolid sodium hydride in a reactor equipped with paddle stirring. Themixture can be maintained at a temperature from about 0° C. and about100° C., preferably from about 60° to about 70° C., for about 1 to about24 hours, preferably from about 1 to about 6 hours, with stirring todisperse the solid. The excess borane can be removed by conventionaldistillation, not shown, to give solid sodium triethoxyborohydride inquantitative yield.

A portion of the triethyl borate obtained from the reaction of equation(9) can be directed to an appropriate pressurized reactor and reactedwith hydrogen gas to provide diborane (B₂H₆) and ethanol, as provided inequation (11).

B(OEt)₃+3H₂→½B₂H₆+3EtOH  (11)

The chemical reaction of equation (11) is endothermic. For example, thisreaction can be performed in an autoclave 210, as illustrated in FIG. 1.In such an apparatus, an autoclave containing triethyl borane can bepressurized with hydrogen gas to about 100-1000 psi (about 6.8 to about68 atm.), preferably from about 14 to about 40 atm., and heated attemperatures ranging from about 100° to about 500° C., preferably fromabout 150° to about 300° C. Typical hydrogenation catalysts, includingRaney nickel and activated palladium, silver, or platinum metals andother Group VIII metals, can be used to promote the reaction. Thealcohol can be condensed from the gas stream and recycled for use inother reactions of the process.

Lastly, the sodium triethoxyborohydride from the reaction of equation(10) can be directed to an appropriate apparatus to react with thediborane from the reaction of equation (11) to obtain sodium borohydrideand triethyl borate, as provided in equation (12).

2NaHB(OEt)₃+B₂H₆→2NaBH₄+2B(OEt)₃  (12)

The chemical reaction of equation (12) is exothermic. For example, thisreaction can be performed in a gravity bed reactor 200, as illustratedin FIG. 1. In such an apparatus, a gas stream of diborane at pressuresranging from about atmospheric pressure to about 100 psi (6.8 atm.),preferably from about 1 to about 2 atm., can be passed through sodiumtriethoxyborohydride at temperatures ranging from about −30° C. to about150° C., preferably from about 70° C. to about 120° C., under an inertatmosphere, such as nitrogen or argon gas. The by-product triethylborate can be removed by any method or process known to one skilled inthe art, e.g., by distillation or separation by gravity, to leave sodiumborohydride in quantitative yield. The separated triethyl borate canthen be recycled for use in the reaction of equation (11) as shown inFIG. 1 and/or in the reaction of equation (10) to produce sodiumtriethoxyborohydride.

The reactants for the chemical reactions of equations (9)-(12) can bepurchased from commercial sources or, more preferably, can besynthesized in the process plant. In one embodiment of the presentinvention, sodium borate used in equation (9) can be obtained bypurifying borate ore, e.g., mixing the borate ore in a mixing tank whilecooling, centrifuging out any undesired materials, and drying thepurified borate ore.

This process is illustrated in FIG. 1 as follows. Sodium borate is fedinto a crystallizer 10. Some of this sodium borate passes in a recycleloop through a chiller 20, then passes into a centrifuge 30 to furtherpurify it. Impurities from the centrifuge are passed through an ionexchange column 40 and then disposed. The purified sodium borate is thenpassed into a rotary dryer 50.

The sodium hydride (NaH) used in equation (10) and the hydrogen used inequation (11) can also be synthesized in the process plant, as follows.The sodium bicarbonate produced in equation (9) can be directed to asuitable vacuum dryer to produce sodium oxide (Na₂O), carbon dioxide andwater, as provided below in the chemical reaction of equation (5c)wherein Y is sodium.

2NaHCO₃→Na₂O+2CO₂+H₂O  (5c)

For example, this reaction can be performed in a rotary calciner 140,which is commercially available from the Bethlehem Corporation. In suchan apparatus, a slurry of sodium bicarbonate can be heated to betweenabout 400° and about 1000° C., preferably from about 800° to about 900°C., in a rotary dryer with a heated screw agitator, which is capable ofdispersing the slurry along the length of the reactor. The hightemperature allows the steam to be driven off the solid sodium oxide.

The sodium oxide can then be reacted with methane in a suitableapparatus to provide sodium, carbon monoxide and hydrogen, as shown inequation (14).

Na₂O+CH₄→2Na+CO+2H₂  (14)

The chemical reaction of equation (14) is endothermic. For example, thisreaction can be performed in an autoclave 150. In such an apparatus,solid sodium oxide can be heated to from about 500° to about 1200° C.,preferably from about 900° to about 1100° C., in an autoclave equippedwith turbine stirring, and the reactor pressurized with methane gas atfrom about atmospheric pressure (1 atm.) to about 1000 psi (68 atm.).The solid can be stirred and heated under this atmosphere, and theproduct gas stream can be cooled to a temperature from about 100° toabout 800° C., preferably from about 100° to about 400° C., to allowseparation of molten sodium. The gas stream containing carbon monoxideand hydrogen can then be directed to an appropriate apparatus, such as ashift reactor 170, for reaction of carbon monoxide with steam to produceadditional hydrogen gas, as described below.

The methane (natural gas), used in the reaction of equation (14), can bepurchased from commercial sources. The sodium produced in the reactionof equation (14) can be easily removed from the other gaseouscomponents, and carbon monoxide can also be removed by using anappropriate apparatus, as provided below in equation (15).

CO+H₂O→CO₂+H₂  (15)

For example, this reaction can be performed in a shift reactor 170. Asis well-known to the skilled artisan, such an apparatus allows thereaction of CO and steam by passing the gas stream over iron and coppercatalysts at approximately 425° C. to produce hydrogen and carbondioxide.

Additional hydrogen gas can be produced by steam reforming of methane asshown in equation (16).

CH₄+H₂O→3H₂+CO  (16)

For example, this reaction can be performed in a steam reformer 155, asillustrated in FIG. 1. As is well known to the skilled artisan, methanecan be mixed with steam at temperatures from about 450° to about 750° C.and pressures from about 30 to about 40 atmospheres as it enterscatalyst tubes containing a nickel catalyst to produce a gas stream ofhydrogen and carbon monoxide. The hot gas stream can then be passedthrough a heat exchanger to provide process heat. Note that the carbonmonoxide produced in this reaction can also be used in the reaction ofequation (15) to provide additional hydrogen.

The hydrogen produced in the reactions of equations (15) and (16) can bedivided into two portions. One portion can be used in the chemicalreaction of equation (11) in apparatus 210. The other portion can beused to react with the sodium obtained in equation (14) to providesodium hydride (NaH) in an appropriate apparatus as shown below inequation (17).

2Na+H₂→2NaH  (17)

The sodium hydride can then be used in chemical reaction of equation(10) in apparatus 190. For example, the reaction shown in equation (17)can be performed in an autoclave 180. In such an apparatus, moltensodium can be cooled to a temperature from about 100° and to about 800°C., preferably from about 100° to about 400° C., before being introducedinto an autoclave equipped with turbine stirring. The reactor can bepressurized with hydrogen gas, ranging from about atmospheric pressure(−1 atm.) to about 1000 psi (68 atm.), preferably from about 5 to about20 atm., and the molten sodium can be agitated to facilitate thoroughmixing. Since NaH is a solid, it can be easily separated by any methodand/or process known to the skilled artisan.

The net equation represented by the equations (9) through (17) is shownin equation (18) as follows:

NaBO₂+CH₄→NaBH₄+CO₂  (18)

The overall equation is endothermic, where the steps represented byequations (9), (11), (14), and (16) are the key energy-consuming stepsof the process. Thermodynamic values for each of the reactions in thisembodiment are shown below. All thermodynamic values are taken from theCRC Handbook of Chemistry and Physics, 69th Edition, 1988-1989, which isincorporated herein by reference. The overall process of this embodimentis also favorable in that it is a cyclic process best represented by thelisting of all reactions below. As shown, the reaction can consume onlymethane and borate to produce sodium borohydride and carbon dioxide. Allother reagents can be generated within the process.

BTU/ lb NaBH₄ 2 NaBO₂ + CO₂ + ½ H₂O → NaHCO₃ + ½ Na₂O.2B₂O₃ ½Na₂O.2B₂O₃ + 6EtOH → 2B(OEt)₃ + 2NaOH + 2.5 H₂O NaHCO₃ → ½ Na₂O + CO₂ +½ H₂O NaOH → ½ Na₂O + ½ H₂O 831 BTU (877 kJ) CH₄ + Na₂O → 2Na + CO + 2H₂ 1642 BTU (1732 kJ) 2Na + H₂ → 2NaH 2B(OEt)₃ + 2NaH → 2NaHB(OEt)₃CH₄ + H₂O → 3H₂ + CO 856 BTU (903 kJ) 2CO + 2H₂O → H₂ + 2CO₂ 2B(OEt)₃ +6H₂ → B₂H₆ + 6EtOH 2991 BTU (3155 kJ) 2NaHB(OEt)₃ + B₂H₆ → 2NaBH₄ +2B(OEt)₃ Overall: 2NaBO₂ + 2CH₄ → 2NaBH₄ + 2CO₂ 7528 BTU (7941 kJ)

For illustrative purposes, sodium borohydride can be reacted with waterto produce hydrogen gas. The energy equivalent of hydrogen gas is about50,957 BTU per pound. Since each pound of sodium borohydride cantheoretically produce about 0.211 pounds of hydrogen gas, each pound ofsodium borohydride can theoretically yield about 10,752 BTU. The actualcost of producing borohydride can be found by adding 7528 BTU from theabove process, 1130 BTU (resulting from 15% plant inefficiency), and9094 BTU (the energy equivalent of methane), giving a total of 17,752BTU required to produce sodium borohydride in the plant. According tothis calculation, the energy efficiency of producing sodium borohydrideaccording to this embodiment of the present invention (e.g., thecomparison of the energy needed for production versus the energyprovided) would be about 61% (10,752/17,752×100).

This is an improvement over commercial processes that generate sodiumborohydride from sodium or sodium-based compounds. Calculated on a perpound of sodium borohydride produced basis, the process shown inequation (1) requires the energy equivalent of 4,547 BTU of methane andan additional 18,476 BTU of energy to drive the reactions. Assuming 15%inefficiency in the plant, e.g., 2,770 BTU of energy is lost in normalplant operation, the total energy required is about 25,793 BTU. Theresulting energy efficiency of the process is about 42%(10,752/25,793×100).

In another embodiment of the present invention, as illustrated in FIG.2, YBO₂ is chosen to be sodium borate (NaBO₂) and HX is chosen to beROH, i.e. an alcohol. In this embodiment, borate is converted to atrialkyl borate via a borax intermediate. The trialkyl borate is thenconverted to diborane, which is known to disproportionate to borohydrideunder appropriate reaction conditions. This process can be furtherdescribed in part by the following set of chemical reactions andformulae.

In the first step, borax is prepared by acidic dehydration of sodiumborate with carbon dioxide as shown in equation (9a). Mineral acids canbe used as alternatives, but will eliminate the carbon dioxide to sodiumbicarbonate recycle loop.

2NaBO₂+2CO₂+½H₂O→NaHCO₃+½Na₂O·2B₂O₃  (9a)

For example, this reaction can be performed in a stirred tank reactorwith a water-heated jacket 230, as illustrated in FIG. 2. In such anapparatus, a slurry of sodium borate and water can be stirred in areactor equipped with paddle type stirring at temperatures ranging fromabout room temperature to about 250° C., preferably from about 175° toabout 200° C. The reactor can be pressurized with carbon dioxide at apressure from about 10 psi (0.68 atm.) to about 750 psi (51 atm.),preferably from about 30 to about 40 atm. The borax produced can beremoved from the reactor by any method or process known to one skilledin the art, such as by filtration.

The borax produced in the reaction of equation (9a) can then be reactedwith a lower alkanol, such as methanol, in an appropriate reactor, asshown in equation (19).

½Na₂O·2B₂O₃+6CH₃OH→2B(OCH₃)₃+NaOH+2.5H₂O  (19)

For example, this reaction can be performed in a stirred tank reactorwith a water-heated jacket 240. Solid borax can be heated to atemperature from about room temperature to about 100° C., preferablyfrom about 55° to about 70° C., as a slurry in methanol for about 1 toabout 6 hours in a reactor equipped with paddle type stirring. Theresulting trimethyl borate can be removed as it forms by any method orprocess known to one skilled in the art, such as by distillation.

The reactions of equations (9a) and (19) can be taken separately orcombined into one step to directly convert NaBO₂ to B(OCH₃)₃ in methanolwith carbon dioxide as shown in equation (20). The combined process isexothermic and can be driven to completion by continuous distillation oftrimethyl borate from the reactor, not shown.

NaBO₂+CO₂+3CH₃OH→B(OCH₃)₃+NaHCO₃+H₂O  (20)

Both versions are encompassed by this embodiment of the presentinvention. Diborane can then be produced by direct hydrogenation of thetrimethyl borate, which can be obtained from the reactions of equations(19) and/or (20). After separation from the other products of reactions(19) and/or (20) by any method or process known to the skilled artisan,the trimethyl borate can be reacted with hydrogen gas in a pressurizedapparatus to produce diborane and methanol, as shown in equation (21).

2B(OCH₃)₃+6H₂→B₂H₆+6CH₃OH  (21)

For example, this reaction can be performed in an autoclave 250, asillustrated in FIG. 2. An autoclave containing trimethyl borate can bepressurized with hydrogen gas at a pressure from about 100 (6.8 atm.) toabout 1000 psi (68 atm.), preferably from about 7 to about 15 atm., andheated at temperatures ranging from about 100° to about 500° C.,preferably from about 200° to about 300° C. Typical hydrogenationcatalysts, including Raney nickel and activated palladium, silver, orplatinum metals and other Group VIII metals, can be used to promote thereaction. The methanol can be separated from the gas stream by anyprocess or method known to the skilled artisan, such as by condensation,and recycled in the process.

Diborane can undergo asymmetric cleavage and subsequentdisproportionation as shown in reaction (22) through (24) by reactionwith any small, hard base, such as F⁻, OH⁻, O⁻², CO₃ ²⁻, NH₃, Cl⁻,CH₃NH₂, and (CH₃)₂NH. Additional examples of hard bases are provided inShriver et al., Inorganic Chemistry (1990, W. H. Freeman Company), whichis incorporated herein by reference. Preferred bases are the oxide, thehydroxide and the carbonate. In concentrated aqueous sodium hydroxide,for example, at reduced temperatures, e.g., from about −20° C. to about20° C., preferably at about 0° to 5° C., the disproportionation occursin two steps: (i) asymmetric cleavage into a borohydride anion and a BH₂⁺ fragment which coordinates two hydroxides and then (ii)disproportionation of the two BH₂ ⁺ fragments into an additionalborohydride anion and a tetrahydroxyborate ion. Preferably, in thisreaction, there are between about 0.1 and 10 molar equivalents of thebase for every molar equivalent of diborane present in the rector.

Water can be replaced with a nonaqueous aprotic solvent or a nonaqueouspolar solvent in the above-described reaction to minimize competitivehydrolysis of the BH₂ ⁺ fragment and allow the disproportionation to beachieved with higher efficiency, thereby providing greater yield.Hydrolysis, on the other hand, results in the release of hydrogen ratherthan disproportionation, and a substantial energy loss occurs. Examplesof acceptable nonaqueous aprotic solvents include, without intendedlimitation, hydrocarbons, such as, hexane or heptane; amides, such as,dimethylacetamide; and glymes, such as, diethylene glycol dimethyl ether(diglyme) and tetra(ethylene glycol) dimethyl ether (tetraglyme).Examples of suitable nonaqueous polar solvents include, without intendedlimitation, methanol, ethanol, propanol, isopropanol, and ionic liquidssuch as imidazolium, pyridinium, phosphonium, and tetralkylammoniumcompounds.

Alternatively, this reaction can be accomplished without the use of asolvent, as illustrated by the chemical reactions of equation (22)through (24). A gas stream of diborane obtained from reaction (22) canbe passed through or over solid base in an appropriate apparatus, e.g. afluidized bed, a ball mill, or other apparatus capable of agitating thereaction mixture. Diborane is an extremely reactive compound, and isknown to react from the gas stream.

2B₂H₆+2Na₂O→3NaBH₄+NaBO₂  (22)

2B₂H₆+4NaOH→3NaBH₄+NaBO₂+2H₂O  (23)

2B₂H₆+2Na₂CO₃→3NaBH₄+NaBO₂+2CO₂  (24)

For example, this reaction can be performed in a fluidized bed reactor270 in the absence of a solvent or a jacketed stirred tank reactor, notshown, with a nonaqueous solvent as described above. A preferrednonaqueous solvent is a glyme, such a diglyme. The reaction ispreferably carried out at a temperature between about −5° C. and 100° C.and at pressures between about 14 psi (1 atm) and 200 psi (13.6 atm),preferably between about 14 psi (1 atm) and 100 psi (6.8 atm).Preferably, the reaction is carried out at a temperature between about70° C. and 80° C. for from about 30 seconds to 100 hours. For each moleof diborane in the reaction medium, there are between about 0.1 and ten,preferably between about five and ten, molar equivalents of the base.

Alternatively, in a reactor equipped with paddle type stirring and ajacket that allows water heating or cooling, diborane can be bubbledthrough a slurry or suspension of the base in a nonaqueous aproticsolvent or nonaqueous polar solvent as described above, preferably in aglyme, at temperatures ranging from about −30° C. and 120° C.,preferably from about 70° C. and 80° C. Such a reactor canadvantageously be incorporated into a process for the generation ofdiborane in that the product can be introduced directly into thereactor, thereby eliminating the need to store large quantities ofdiborane. The reaction is carried out under an inert atmosphere, such asnitrogen or argon gas for from about 30 seconds to about 70 hours. Foreach mole of diborane in the reaction medium, there are between aboutone and ten, preferably between about five and ten, molar equivalents ofthe base. The resulting sodium borohydride can then be separated fromsodium borate by any process or method known to the skilled artisan,such as by liquid extraction. The separated sodium borate can berecycled for use in the initial step of the process, i.e., the reactionof equation (9a).

The reactants for the process of this embodiment can be purchased fromcommercial sources, or preferably, generated in the process plant aspreviously described. For example, the carbon dioxide used in thereaction of equation (9a) and the oxide base, the hydroxide and thecarbonate are all commercial available or may be readily prepared byknown techniques utilizing known starting materials. The sodium oxideused in the reaction of equation (22) can be obtained by converting thesodium bicarbonate generated in the reaction of equation (9a) orequation (20) in an appropriate apparatus, as shown in equation (5c)wherein Y is sodium. The reaction dehydrates the NaHCO₃ and isendothermic.

2NaHCO₃→Na₂O+2CO₂+H₂O  (5c)

For example, the conversion can be performed in a rotary calciner (kiln)260, such as a model manufactured by the Bethlehem Corporation. A slurryof sodium bicarbonate can be heated to a temperature from 400° C. and1000° C., preferably from about 800° C. and 900° C., at a pressure fromabout 0 to about 5 atm., preferably from about 0 to about 1 atm., in arotary dryer with a heated screw agitator, which disperses the slurryalong the length of the reactor. Solid sodium oxide can be separatedfrom a gas stream of carbon dioxide and steam by any method or processknown to the skilled artisan.

The sodium carbonate used in the reaction of equation (24) can beobtained by converting the sodium bicarbonate generated in the reactionof equation (9a) or equation (20) in an appropriate apparatus, as shownin equation (5ci).

2NaHCO₃→Na₂CO₃+2CO₂+H₂O  (5ci)

The conversion of NaHCO₃ into the above-described end products alsodehydrates the NaHCO₃ by thermal decomposition (i.e., heating), but at alower temperature than the reaction of equation (5c). Preferably,reaction (5ci) is conducted at a temperature from about 50° to about120° C. in an appropriate apparatus, such as a rotary dryer. Dehydrationof sodium bicarbonate can be performed between 0 and 1 atmospheres. Thesolid Na₂CO₃ is removed from the gaseous steam and carbon dioxide by anymethod or process known in the art.

Furthermore, the hydrogen gas used in the chemical reaction of equation(22) can be obtained by steam reforming of methane, as described inequation (16).

CH₄+H₂O→3H₂+CO  (16)

For example, this reaction can be performed in a steam reactor 210, asillustrated in FIG. 2. As is well known to the skilled artisan, methanecan be mixed with steam at temperatures of about 450° C. to 750° C. forand pressures from about 30 to about 40 atmospheres as the mixtureenters catalyst tubes containing nickel catalyst to produce a gas streamof hydrogen and carbon monoxide. The hot gas stream can then be passedthrough a heat exchanger to provide process heat if needed. Carbondioxide may also be obtained from the reaction with diborane wherein thebase is a carbonate, as shown in equation 30. The water used in thisreaction can be obtained from commercial sources, the water produced bythe chemical reaction of equation (19) in apparatus 240, and/or thereaction of equation (5ci) in apparatus 260. The methane can be obtainedfrom commercial sources.

The carbon dioxide used in the chemical reaction of equation (9a) can beobtained from the reaction of equation (15). Additional carbon dioxidecan also be obtained by processing the carbon monoxide obtained from thechemical reaction of equation (16) in an appropriate apparatus, asillustrated by equation (15).

CO+H₂O→CO₂+H₂  (15)

For example, this reaction can be performed in a shift reactor 220, asillustrated in FIG. 2. As is well-known to the skilled artisan, such anapparatus allows the reaction of CO and steam by passing the gas streamover iron and copper catalysts at about 425° C. to produce hydrogen andcarbon monoxide. The hydrogen produced by this reaction can be used inthe chemical reaction of equation (21). The water used in this reactioncan be obtained from commercial sources, from the water produced by thechemical reaction of equation (19) in apparatus 240, and/or the reactionof equation (5ci) in apparatus 260.

The net equation of this embodiment is the same as the first embodiment:

NaBO₂+CH₄→NaBH₄+CO₂  (18)

The steps represented by equations (21), (5c) and (16) are the keyenergy-consuming steps of the process. Calculated on a per pound ofsodium borohydride produced basis, this reaction requires the energyequivalent of 9094 BTU of methane and an additional 6701 BTU of energyto drive the reactions. Assuming 15% inefficiency in the plant,approximately 1005 BTU of energy is lost as a result of normal plantoperation. The total energy required by the system to practice thechemical reaction of equation (13) is about 16,800 BTU per pound ofsodium borohydride produced. According to the calculation describedearlier, the energy efficiency of the sodium borohydride (e.g., thecomparison of the energy needed for production versus the energyprovided) would be 64% (10,752/16,800×100).

The energy required for the individual reactions is shown below.

BTU/ lb NaBH₄ 4NaBO₂ + 4CO₂ + → 4NaHCO₃ + 12CH₃OH +4 B(OCH₃)₃ + 4 H₂O4NaHCO₃ → 4Na₂O + 4CO₂ + 1707 BTU 2H₂O (1801 kJ) 4B(OCH₃)₃ + 12H₂ →2B₂H₆ + 12CH₃OH 3282 BTU (3463 kJ) 3CH₄ + 3H₂O → 9H₂ + 3CO 1712 BTU(1806 kJ) 3CO + 3H₂O → 3H₂ + 3CO₂ 2Na₂O + 2B₂H₆ → 3NaBH₄ + NaBO₂Overall: 3NaBO₂ + 3CH₄ → 3NaBH₄ + 3CO₂ 6701 BTU (7070 kJ)

The overall process of this embodiment is also favorable in that it is acyclic process best represented by the listing of all reactions above.As shown, the reaction consumes only methane and borate and producesonly sodium borohydride and carbon dioxide. All other reagents can beregenerated within the process. Thus, the process represents a closedloop, requiring only the input of methane and energy.

Alternatively, diborane used in the chemical reaction of equation (23)can be obtained by reacting a boric oxide with a halogen gas, such aschlorine, and then hydrogenating the resulting boron trihalide, asillustrated in the reactions of equations (25a) and (25b).

2B₂O₃+6X₂+3C→4BX₃+3CO₂  (25a)

4BX₃+12H₂→2B₂H₆+12HX  (25b)

wherein X is selected from the group consisting of F, Cl, Br, and I.Reactions of boric oxides are well-known in the art, as described inHughes, “Production of the Boranes and Related Research,” p. 3.

Typically, BX₃ can be obtained by heating solid boric oxide and carboncoal to a temperature between about 250° and about 850° C., preferablybetween about 600° and about 700° C., in an autoclave under a halogengas atmosphere. The reactor can be pressurized with halogen gas, at apressure of from between about atmospheric pressure (I atm.) to about500 psi (34 atm.), preferably from between about 5 and 10 atm. The borontrihalide can be condensed from the gas stream and isolated as a liquidby any method and/or process known to the skilled artisan.

The use of excess carbon allows the in situ reduction of carbon dioxideto carbon monoxide as illustrated by the following chemical reaction:CO₂+C→2CO. The resulting carbon monoxide can then be introduced into ashift reactor to react with steam to produce additional processhydrogen.

Diborane can also be obtained from hydrogenation of alkylboranes, whichare prepared by reacting boron trihalides with organoaluminum compoundsor Grignard reagents of the formula RMgX, wherein R is a C₁₋₄ alkyl, andX is Cl, Br, or I. Such reactions are well-known in the art, asdescribed in Shriver et al., Inorganic Chemistry (1990, W. H. FreemanCompany), which is incorporated herein by reference. An example of thistype of reaction is shown below in reactions (25c) and (25d). In thesereactions, liquid boron trihalide (BX₃) can be added to solidalkylaluminum under an inert atmosphere in a stir-tank reactor equippedwith turbine stirring at a temperature from about −30° C. and 100° C.,preferably from about 20° C. and 50° C. The alkylborane can be removedby distillation, and thereafter hydrogenated.

2BX₃+Al₂(R)₆→2AlX₃+2BR₃  (25c)

4BR₃+12H₂→2B₂H₆+12HR  (25d)

wherein each R is independently selected from the group consisting ofCH₃ and C₂H₅.

It should be noted that the above processes for obtaining a Y-containingbase and a boron-containing compound can be combined with either of thetwo ways of producing a Y-borohydride and carbon dioxide. One embodimentof one possible combination is shown in the reactions below:

BTU/ lb NaBH₄ 4NaBO₂ + 4CO₂ + → 4NaHCO₃ + 12CH₃OH +4 B(OCH₃)₃ + 4 H₂O4NaHCO₃ → 4Na₂O + 4CO₂ + 1707 BTU 2H₂O (1801 kJ) CH₄ + Na₂O → 2Na + CO +2 H₂ 1641 BTU (1731 kJ) 2Na + H₂ → 2NaH 2B(OMe)₃ + 2NaH → 2NaHB(OMe)₃CH₄ + H₂O → 3H₂ + CO 807 BTU (851 kJ) 2CO + 2H₂O → 2H₂ + 2CO₂ 2B(OMe)₃ +6H₂ → B₂H₆ + 6MeOH 3430 BTU (3619 kJ) 2NaHB(OMe)₃ + → 2NaBH₄ + 2B(OMe)₃B₂H₆ Overall: 2NaBO₂ + 2CH₄ → 2NaBH₄ + 2CO₂ 7585 BTU (8002 kJ)

In this process, 15% plant inefficiency leads to a loss of about 1138BTU (1200 kJ). This number must be added to about 7585 BTU (8002 kJ)necessary for the above reactions, and about 9094 BTU (9594 kJ) for theenergy equivalent of methane. Thus, the overall energy needed for thisplant process requires about 17,817 BTU (18,796 kJ), and the overallefficiency of the process is about 60% (10,752 BTU/17,817 BTU×100).

In another embodiment, X is chosen to be chlorine. Boric oxide can bereacted with carbon and chlorine gas to obtain boron trichloride. Thehydrogen chloride byproduct from the boron trichloride hydrogenation isconverted to chlorine gas by reaction with oxygen and catalytic CuCl,which is nonstoichiometric and is not consumed in the process. Thesereactions are shown below, with the reactions involving the recycle loopshown in boldface.

B₂O₃ + {fraction (3/2)} C + 3Cl₂ → 2BCl₃ + {fraction (3/2)} CO₂ CH₄ +Na₂O → 2Na + CO + 2H₂ 2Na + H₂ → 2NaH 2BCl₃ + 2NaH → 2NaHBCl₃ CH₄ + H₂O→ 3H₂ + CO 2CO + 2H₂O → 2H₂ + 2CO₂ 2BCl₃ + 6H₂ → B₂H₆ + 6HCl 6HCl +{fraction (3/2)} O₂ + CuCl(solid) → 3Cl₂ + 3H₂O 2NaHBCl₃ + B₂H₆ →2NaBH₄ + 2BCl₃ Overall: 2NaBO₂ + 2CH₄ + {fraction (3/2)} C + {fraction(3/2)} O₂ → 2NaBH₄ + {fraction (7/2)} CO₂

Carbon dioxide can be reclaimed from the boric oxide, carbon, andchlorine reaction shown in boldface above. In the presence of excesscarbon, carbon dioxide is converted to carbon monoxide through thereaction as described above. The carbon monoxide can then be introducedinto the shift reactor for preparation of additional hydrogen. Ideally,this would occur in one step as shown below in equation (26):

B₂O₃+3C+3Cl₂→2BCl₃+3CO.  (26)

Methane can be used instead of carbon in a variation on the route shownabove. A stream of methane gas passed through hot boric oxide willgenerate carbon and hydrogen gas in the reactor. Ideally, this processwould be coupled with direct hydrogenation of boron trichloride toproduce diborane. This variation is shown below, with the recycle loopsin boldface.

2 NaBO₂ + CO₂ + ½ H₂O → NaHCO₃ + ½ Na₂O.2B₂O₃ ½ Na₂O.2B₂O₃ → ½ Na₂O +B₂O₃ NaHCO₃ → ½ Na₂O + CO₂ + ½ H₂O B₂O₃ + {fraction (3/2)} CH₄ + 3Cl₂ →2BCl₃ + {fraction (3/2)}CO₂ + H₂ 2BCl₃ + 6H₂ → B₂H₆ + 6HCl CH₄ + Na₂O →2Na + CO + H₂ 2Na + H₂ → 2NaH 2BCl₃ + 2NaH → 2NaHBCl₃ CH₄ + H₂O → 3H₂ +CO 2CO + 2H₂O → 2H₂ + 2CO₂ 6HCl + {fraction (3/2)} O₂ + CuCl(solid) →3Cl₂ + 3H₂O 2NaHBCl₃ + B₂H₆ → 2NaBH₄ + 2BCl₃ Overall: 2NaBO₂ + {fraction(7/2)} CH₄ + {fraction (3/2)} O₂ → 2NaBH₄ + {fraction (7/2)} CO₂ + 3H₂

Alternative methods to produce boron trichloride would use other knownchlorinating agents beside hydrogen chloride and chlorine, which are thepreferred reagents. Other possible chlorinating agents include phosgene(COCl₂) and methods to generate phosgene in situ (such as by addingcarbon monoxide to chlorine gas), phosgene equivalents includingdiphosgene (trichloromethylchloroformate) and triphosgene(bis(trichloromethyl)carbonate), thionyl chloride (SOCl₂), andphosphorus chlorides including phosphorus trichloride and phosphoruspentachloride.

Another possible embodiment of the present invention involves using bothchlorine and the methoxy group as “X” in the reactions. This set ofreactions, shown below, allows for recycle loops involving both hydrogenchloride and B(OMe)₃. Reactions involving recycle loops are printed inboldface.

2 NaBO₂ + CO₂ + ½ H₂O → NaHCO₃ + ½ Na₂O.2B₂O₃ ½ Na₂O.2B₂O₃ → ½ Na₂O +B₂O₃ NaHCO₃ → ½ Na₂O + CO₂ + ½ H₂O B₂O₃ + {fraction (3/2)} C + 3Cl₂ →2BCl₃ + {fraction (3/2)} CO₂ Na₂O + CH₄ → 2Na + CO + 2H₂ CH₄ + H₂O →CO + 3H₂ 2CO + 2H₂O → 2H₂ + 2CO₂ 2Na + H₂ → 2NaH 2NaH + 2B(OMe)₃ →2NaHB(OMe)₃ 2BCl₃ + 6H₂ → B₂H₆ + 6HCl 6HCl + {fraction (3/2)} O₂ +CuCl(solid) → 3Cl₂ + 3H₂O B₂H₆ + 2NaHB(OMe)₃ → 2NaBH₄ + 2B(OMe)₃Overall: 2NaBO₂ + 2CH₄ + {fraction (3/2)} C + {fraction (3/2)} O₂ →2NaBH₄ + 3.5 CO₂

What is claimed is:
 1. A process for producing borohydride compoundsrepresented by the formula YBH₄, comprising: (A) reacting aboron-containing compound represented by the formula BX₃ with hydrogenor an aldehyde selected from the group consisting of formaldehyde,benzaldehyde, acetaldehyde, and mixtures thereof to obtain diborane; and(B) reacting the diborane with a Y-containing base selected from thoserepresented by the formula Y₂O, YOH and Y₂CO₃ to obtain YBH₄ and YBO₂,wherein Y is selected from the group consisting of the alkali metals,pseudo-alkali metals, alkaline earth metals, an ammonium ion, andquaternary amines of the formula NR₄ ⁺, wherein each R is independentlyselected from hydrogen and a straight- or branched-chain C₁₋₄ alkylgroup; and wherein X is selected from the group consisting of halideions, —OH, —R′ and —OR′ groups, chalcogens, and chalcogenides, whereinR′ is a straight- or branched-chain C₁₋₄ alkyl group.
 2. A process inaccordance with claim 1, wherein Y is selected from the group consistingof Na⁺, Li₊, K⁺, Mg₊₊ and Ca⁺⁺ and X is selected from the groupconsisting of a halide ion and —OR′.
 3. A process in accordance withclaim 1, wherein the Y-containing base represented by the formula Y₂O,and the boron-containing compound of formula BX₃ are obtained by aprocess comprising: reacting a borate of the formula YBO₂ with CO₂ andan alcohol to obtain YHCO₃ and BX₃; and converting the YHCO₃ to Y₂O byheating to a temperature from about 400° to about 1000° C., wherein X isan −OR′ group.
 4. A process in accordance with claim 3, wherein Y issodium and said borate is represented by the formula Na₂O·xB₂O₃·yH₂O,wherein x is 1 to 5 and y is 0 to
 10. 5. A process in accordance withclaim 1, wherein the Y-containing base is represented by the formulaY₂CO₃, and the boron-containing compound of formula BX₃ are obtained bythe process comprising: reacting a borate of the formula YBO₂ with CO₂and an alcohol to obtain YHCO₃ and BX₃; and converting the YHCO₃ toY₂CO₃ at a temperature from about 50° to about 120° C. wherein X is an—OR′ group.
 6. A process in accordance with claim 5, wherein Y is sodiumand said borate is represented by the formula Na₂O·xB₂O₃·yH₂O, wherein xis 1 to 5 and y is 0 to
 10. 7. A process in accordance with claim 1,wherein, in step (A), BX₃ is reacted with hydrogen.
 8. A process inaccordance with claim 1, wherein in step (B), said base is Y₂CO₃, thereaction is carried out in an aqueous solution of said base at atemperature of from about −5° C. to about 20° C. and said solutioncontains from about 0.1 to 10 molar equivalents of said base for everymolar equivalent of diborane present.
 9. A process for producingborohydride compounds represented by the formula YBH₄, comprisingreacting gaseous diborane in the absence of solvent with a Y-containingbase selected from those represented by the formula Y₂O, YOH and Y₂CO₃to obtain YBH₄ and YBO₂, wherein Y is selected from the group consistingof the alkali metals, pseudo-alkali metals, alkaline earth metals, anammonium ion and quaternary amines of the formula NR₄ ⁺, wherein each Ris independently selected from hydrogen and a straight- orbranched-chain C₁₋₄ alkyl group.
 10. A process in accordance with claim8 further comprising agitating the gaseous diborane and the base duringthe reaction.
 11. A process in accordance with claim 10, wherein saidgaseous diborane and said base are agitated in a ball mill during saidreaction.
 12. A process in accordance with claim 9, wherein Y isselected from the group consisting of Na⁺, Li⁺, K⁺, Mg⁺⁺ and Ca⁺⁺.
 13. Aprocess in accordance with claim 9, wherein diborane and said base arereacted at a temperature between about −5° C. and about 100° C. for fromabout 30 seconds to about 100 hours.
 14. A process in accordance withclaim 9, wherein from about 0.1 and about ten molar equivalents of saidbase are present for every molar equivalent of diborane.
 15. A processin accordance with claim 9, wherein diborane and said base are reactedat a pressure between about 14 psi and about 200 psi.
 16. A process forproducing borohydride compounds represented by the formula YBH₄,comprising reacting gaseous diborane with a Y-containing base insuspension in a nonaqueous aprotic solvent or a nonaqueous polarsolvent, said base being selected from those represented by the formulaY₂O, YOH and Y₂CO₃ to obtain YBH₄ and YBO₂, wherein Y is selected fromthe group consisting of the alkali metals, pseudo-alkali metals,alkaline earth metals, an ammonium ion and quaternary amines of theformula NR₄ ⁺, wherein each R is independently selected from hydrogenand a straight- or branched-chain C₁₋₄ alkyl group.
 17. A process inaccordance with claim 16 further comprising agitating said suspensionduring the reaction.
 18. A process in accordance with claim 17, whereinsaid suspension is agitated in a ball mill during said reaction.
 19. Aprocess in accordance with claim 16, wherein Y is selected from thegroup consisting of Na⁺, Li⁺, K⁺, Mg⁺⁺ and Ca⁺⁺.
 20. A process inaccordance with claim 16, wherein diborane and said base are reacted ata temperature between about −30° C. and about 80° C. for from about 30seconds to about 70 hours.
 21. A process in accordance with claim 16,wherein from about 0.1 and about ten molar equivalents of said base arepresent for every molar equivalent of diborane.
 22. A process inaccordance with claim 16, wherein the non-aqueous solvent is a glyme.